Abatement Work Practices and Engineering Controls
Containment and engineering controls
The goal is to keep fibers inside a controlled area and exhaust filtered air outside. Isolate HVAC and openings with critical barriers-sealed plastic over doors, vents, and penetrations-then build the containment. Use fire-retardant polyethylene (commonly 6 mil), seal seams, and maintain a negative-pressure enclosure with HEPA air scrubbers exhausted outdoors so air flows inward. The project designer specifies air changes; 4 ACH is a common specification, but verify the plan. Post warning signs and set up a decontamination unit at the boundary.
Work practices
Use wet methods throughout: amend water with a surfactant, keep material wet, and mist before breaking. Never dry sweep, use compressed air, or drop debris from height. Use HEPA vacuums and drop cloths. For small pipe sections, a glove bag can confine the work; for large jobs, wrap and remove in sections, then lower in sealed containers. OSHA classifies work as Class I (pipe/boiler insulation and surfacing), Class II (floor tile, roofing, etc.), Class III (repair), and Class IV (cleanup); the class determines required controls. Stop work if the enclosure is breached, and clean up immediately.
Clearance
After removal, the project monitor performs a visual inspection for dust and debris. Many CT projects also require clearance air sampling by PCM, with a common limit of 0.01 f/cc, before the containment comes down. Only then is the area released for reoccupancy. Final cleaning includes HEPA vacuuming and wet wiping of surfaces, not just bagging waste.
Worked example
A crew contains a mechanical room but props the entry door open “for airflow” and uses a box fan to exhaust air. The reasoning: the open door destroys the negative-pressure boundary; the box fan is not HEPA-filtered and can spread fibers; airflow must come from clean to dirty and exhaust through HEPA. Correct by sealing the door, installing a HEPA air scrubber, and using the decon unit for entry/exit.
Traps
Containment is not optional for “small” jobs. Negative pressure is not the same as a fan. Poly sheeting alone does not filter air. Do not remove containment immediately after the last wrap; clearance is required. Do not use dry methods because a HEPA vacuum is present. A glove bag is not a substitute for containment on a large removal.